Photolithographic printing materials



Jan. l0, 1950 c. H. MlTsoN ETAL v 2,494,053

PHOTOLITHOGRAPHIC PRINTING MATERIALS Filed March 17', 1944l F/GJ;

Patented Jan. 10, 1,950

PHOTOLITHOGRAPHIC PRINTING MATERIALS Charles Howard Mitson and ErichEduard Loening, Wealdstone, England, assignors to Eastman Kodak Company,Rochester, N. Y., a corporation of New Jersey Application March 17,1944, Serial No. 526,984 In Great Britain March '22, 1943 14 Claims.

This invention is primarily concerned with the formation of designs insheets to enable them to be used as the printing surfaces for greasyinks in rotary offset printing machines for oflice use, but it is alsoapplicable to the formation of designs in other lithographie(particularly photolithographie) printing materials and in addition tothe formation of designs in materials for other purposes. rThe term"design in this specification is used in the widest sense to includelettering, maps, pictures and any other matter normally capable ofrepresentation by black and white or other contrasting colours.

If parts of a cellulose derivate, e. g. a cellulose acetate, arehydrolysed, their physical properties become different fro-m those ofthe remaining parts. It is known to make use of this fact in thepreparation of printing surfaces, but the processes proposed hithertosuffer from various disadvantages. Thus in a process described inBritish Specification No. 368,083 a photographically produced,chrome-albumen reproduction of the desired design is superposed on ahydrolysable sheet and the hydrolysis takes place over the areas notcovered by this reproduction; it is necessary to protect thechrome-albumen itself from the hydrolysing agent, e. g. by asphalt orlithographie ink (which is a greasy ink), and this introduces diiculty.Again, in a process described in German Specification No. 509,010 acellulose acetate surface is hydrolysed all over and coated with alight-sensitive layer in which the desired image is produced and thenpart of the layer is removed image-Wise so as to leave an image in gumfor printing purposes, but such gum images are liable to Wear out when anumber of prints are taken from them. One reason for this is that inthis process as in that of British Specification No. 368,083, the partsWhichtake the ink are those superposed on the foundation and so areparticularly liable to Wear away, Whereas if the foundation itself takesthe ink and an ink-repellent design is formed the printing propertiescan be maintained much longer.

The present invention is based essentially on the idea of using astencil of the design as a temporary measure to enable some areas of ahydrolysed surface to be so treated that they display surfaces ofdifferent chemical composition, use being directly made of theresulta-nt different properties of the different areas. For our purposesthe eifect of the treatment is the same as if the treated areas wereless hydrolysed than the others. Thus if the product is to be used forphotolithographic printing the areas that are to accept the printing inkmust be of an ink-receptive composition and the remaining areas must behydrolysed to a sufficient degree to repel ink when they are wet. If, onthe other hand, the product is, for instance,.to be differentiallycoloured the areas to be coloured must by virtue of their diiference inchemical composition have the property of absorbing a dye to a greaterextent than thewother areas. l

According to the invention the stencil is superposed on a surface thathas been-uniformly.hy-v drolysed and serves to protect areas of thatsurface while the other areas are selectively removed or lconverted to adiiferent chemical composition and thereafter the stencil is removed tovexpose the protected hydrolysed areas. At .thevtime'of the removal orrconxv/ersion the surface is a uniform .state of hydrolysis, that-is tosay,-is hydrolysed ythroughout the Whole Working surface to asubstantially uniform depth and degree of hydrolysis.

The stencil is preferably photographically produced and it may be formedin situ -or a preformed lstencil may be applied to the hydrolysedsurface, e. g. by a transfer process of the kind used in photography,and if it is formed in situ the surface may .be hydrolysed before theformation of the stencil or hydrolysis may be effected during or afterthe formation of the stencil. If the stencil is formed after thehydrolysis or a preformed stencil is used, a prehydrolysed layer may beusedas the starting material.

In producing a printing surface the hy drolysable substance may be inthe form of a simple ink-receptive layer, and then of course the.

depth of the hydrolysis must be controlled so that there isnon-hydrolysed-material left beneath it to form the ink-receptive areas.Alternatively a multi-layer sheet having a hydrolysable layer as Aa facelayer may be used, and then the-hydrolysis may proceed through the Wholeor only part of the face layer. If it does not penetrate through theWhole of the face layer, the layer or layers underneath simply form areinforcing support, but if it penetrates through the Whole of the facelayer the supporting layer, though it may or may lnot be hydrolysable,must provide the inkreceptive areas of the final surface, and it may forinstance be cellulose nitrate.

In any case, the substance from which the hydrolys-able (or hydrolysed)layer is formed preferably consists of cellulose acetate. However othermaterials may be used, provided that they hydrolyse to give a solid orjelly-like product and that if s. printing surface is being producedthey 3 are ink-receptive and can be hydrolysed to an ink-repellentstate. Further, if the hydrolysis is to be effected before or during theformation of the stencil and an alkaline developer is used thehydrolysed product, while being hydrophilic, must be insoluble in dilutealkali solutions such as are used in developers. Examples of materialswhich may be used instead of cellulose acetates are other esters such ascellulose esters (especially organic esters for instance fatty acidesters e. g. cellulose butyrates and cellulose propionates and anymixture of acetates,n propionates and butyrates of cellulose) and resinsof an ester character. Further examples are polyvinyl acetates,polyvinyl butyrates and polyvinyl propionates, which may be used aloneor mixed with a non-hydrolysable material, e. g. a polyvinyl acetal, inorder to impart additional strength to the final hydrolysed sheet.Cellulose nitrate may also be used if a suiciently strong hydrolysingagent is employed.

Fig. 1 is a sectional view through a multi-layer strip or sheet used informing a stencil;

Fig. 2 is a view similar to Fig. 1 showing the sheet after exposure anddevelopment;

Fig. 3 shows the sheet after the unprotected portions of the hydrolysedlayer are removed to expose the non-hydrolysed layer;

Fig. 4 shows the sheet after the removal of the stencil layer to exposethe previously protected hydrolysed layer;

Fig. 5 is a view similar to Fig. 2 but in which the exposed portions ofthe hydrolysed'layer'are converted to a different chemical composition;

Fig. 6 is a view of the sheet shown in Fig. 5 with the stencil layerremoved;

Fig. '7 is a view similar to Fig. 1 but-showing a multi-layer sheet thelayers of which areY formed of diierent materials, only one of which ishydrolysable;

Fig. 8 shows the strip of Fig. '7 when the hydrolysable layer ishydrolysed and a photographic emulsion layer applied;

Fig. 9 shows a sheet with a metal base coated with a hydrolysable layercarrying a gelatine photographic emulsion;

Fig. l0 shows the sheet of Fig. 9 after the emulsion layer has beenexposed and developed; and

Fig. 11 shows the sheet of Fig. 10 after'V the hydrolysable layer hasbeen hydrolysed.

An example of a process for preparing a printing material in which thesurface is hydrolysed before the formation of the stencil will now bedescribed with reference to Figures 1 to 4 of the accompanying purelydiagrammatic drawings.

The starting material is a single-layer sheet about 0.005" thick of acellulose acetate that has an ink-receptive surface.` This is hydrolysedin an aqueous solution of caustic alkali (50% solution of sodiumhydroxide) for from 2 to 5 minutes to bring about hydrolysis of thesurface to a uniform extent and thus convert the sheet into a layer l(probably less than 0.001" thick), hydrolysed to such an extent thatwhen wet it will repel ink, and a layer 2 that has been unaffected bythe treatment. The alkali is washed out and the sheet is coated with alayer 3 of an unhardened light-sensitive gelatine emulsion containingsilver halide, that is to say, a layer in which a stencil may be formedby photography. The material at this stage is shown in Figure 1. Afterexposure of the layer 3 under a positive of the desired design(preferably through the layer 2) the material is subjected to the actionof a tanning developer. Ihis leads to hardening of the parts on whichthe light has acted, and the unhardened parts of the layer 3 are removedin the usual way, leaving a stencil 4, as shown in Figure 2. The stencilis dried and the areas of the layer I not protected by it are thenremoved. This is done with a solution of zinc chloride (60 B.), which ispoured on the sheet and distributed over its surface, and

. rubbed with cotton wool.

the surface is then immediately and vigorously By this means, areas ofthe layer I are removed and cellulose acetate areas 5 underneath arelaid bare, as shown in Figure 3. These areas 5 match the design andcorrespond, for instance, to the lines of a map. The stencil is thenentirely removed to expose the protected hydrolysed areas havingink-repellent surfaces beneath it; this may be done by treatment with asolution of sodium hypochlorite, and after a short rinsing and removalof the surplus Water the sheet, as shown in Figure 4, presents the lines5 of the design as an engraved intaglio which easily accepts fatty inks,Whereas the surrounding areas E when wet repel the ink.

A particular advantage of the process just described is that thestarting material is a readily available commercial product and that theprocess is simple and produces an excellent printing surface.

In the example described above the hydrolysed areas are removed by beingdissolved and as is indicated by the example this is preferably done bymeans of a solution containing zinc chloride. It may be desirable to addethyl lactate to the zinc chloride, as it serves to etch the acetate andto facilitate the removal of the hydrolysed material. Other solventswhich are suitable for dispersing or dissolving the hydrolysed surfacelayer, such for example as lactic acidor copper ammonium hydroxide orany other cellulose hydrate solvent, may also be used. Alternativelysolvents can be used which do not actually dissolve the hydrolysedsurface layer, but which are able to penetrate this layer and to attackthe layer beneath it, and which thereby loosen the hold of the surfacelayer, which can then be mechanically removed by rubbing. If the layerbeneath consists of cellulose acetate or cellulose nitrate such solventsas acetone, ethyl acetate, amyl acetate or its mixtures are suitable forthis purpose.

Instead of removing the areas 5 they may be converted into a differentchemical composition by treatment with a liquid containing a solvent fora constituent of the material presenting those areas. For instance it isfound that if a solution of Zinc chloride and ethyl lactate (two volumesof Zinc chloride of 55 B. and one volume of commercial ethyl lactate) isused, but the surface is only lightly rubbed with cotton wool wettedwith the solution, the areas 5 undergo some chemical conversion, thenature of which is not at present understood and which may or may notinvolve chemical reaction, but which leaves them ink-receptive. It seemslikely that this change in chemical composition involves an alterationin the ratio of hydrate to ester, possibly by the solvent action of theethyl lactate on the underlying ester with subsequent dispersion of theester throughout the hydrate. However this may be, it will be understoodthat the different areas must be substantially different in theirchemical composition if effective use is to be made of them for printingor other purposes. Thus the material instead of being as shown in Figure3 is as shown in Figure 5, in which the converted' parts are show'n" at2A. The stencil isinextremoved by treatment with a hypochlorite solutionto expose the hydrophilic parts 6, as show-nin Figure 6. Again, a resin,e. g'. a phenolald'ehyd'e resin, dissolved in a solvent for aconstituent of the material may be rubbed over' the surface untill itforms a coating on the hydrolysed areas'. rf course, the resin must beso chosen thatv at' the most it forms on thev stencil only a coatingwhich will permit the subsequent removal of the stencil with the coatingby, for example, ahypochlorite solution. Naturally the resin must be ormust form with the hydrolysed areas an ink-receptive surface if printingplates are being made.

An example of the use of a multi-layer sheet isillustrated in Figures '7and 8. Here there is a supporting layer l of cellulose nitrate or otherink-accepting material that either cannot be hydrolysed' or can behydolysed only with diiculty, and itis covered with a sheet of celluloseacetate 2B or other easily hydrolysable material, this sheet then beinghydolysed throughout its whole depth. Figure 8 shows the material afterthe Whole ofthe acetate layer has been hydrolysed into a layer IB and aphotographic emulsion layer 3` has been applied. Thereafter the methodmay be the same as that described with reference to Figures 2 to 4. Thismethod has the advantage that the hydrolysis is more easily controlledas it cannot easily penetrate further than through theA layer ofvcellulose acetate andthe back of the material is not aifected by thehydrolysis. The support layer 'l will then offer greater mechanicalresistance during the printing operation than a sheet of hydrolysedcellulose acetate, which would normally havel been acted upon at bothsurfaces. Alternatively a protective lacquer may be used on the reverseside' of the cellulose acetate or other hydrolysable layer for the samepurpose.

If the hydrolysis is effectedv after a gelatine stencil has been formed,the hydrolysis takes place through the stencil. The sheet may beimmersed in a` hydrolysing solution, preferably while it is still wetafter being developed with a tanning developer and washed. It is foundthat a gelatine. photographic emulsion does not unduly impede thehydrolysis. This method is illustrated in Figures 9, 1'0 and 11. Figure9 shows a cellulose acetate layer 2C carried by a support l of cellulosenitrate or metal, e'. g. zinc, and coated with a layer 3 of a gelatineemulsion containing a silver halide. After an image has been formed anddeveloped in a tanning developer the untanned parts are removed so thata stencil 4 is formed as shown in Figure l0. Next the whole sheet isimmersed in a hydrolysing solution. Care must be taken not to soften ordestroy the stencil, which is needed for the subsequent operations.Concentrated' caustic solutions (20 to 50%) are unsuitable but efficienthydrolysis can be effected by solutions of low concentration, e. g. 2%,especially if they are mixed with solvents capable of penetrating intothe surface of cellulose acetate, for example, alcohol or acetone. As anexample the following solution can be used:

Cc. sodium hydroxide 200 Commercial alcohol 400 Acetone v r 10 Water to1,000

The sheet is immersed in such a solution until the desired state ofhydrolysis is obtained, the necessary time usually being from 5 to 10minutes.

Cil

The resultant sheet with the whole acetate layer- 2C so hydrolysedconverted into a layer IC' is shown in-Figure 11.v The remainingstepsmay be as described with reference to Figures 3 and 4.

If the hydrolysis is effected duringv the formation of the stencil, asolution may be usedv which acts'. simultaneously as a tanning developerand as a hydrolysing agent, consisting,.for example', of equal parts ofa 2.5% aqueous solution of pyrocatecholv and a solution containing:

Cc. 2% sodium hydroxide 500 Commercial alcohol 450 Acetone 50 The alkalicontent of this developer being unusually high, the tanning action ofthe developer should be interrupted after, say, 30' to 40 seconds by'the addition of strong sodium sulphite solution, and in order to'allowsufficient time for the hydrolysis the sheet may remain for further 4 to5 minutes in the developer if necessary.

In these methods in' which the hydrolysis takes place during or afterthe formation of the` stencil the substance that is hydrolysed' must notbe one which is so dincult tohydrolyse that it requires such a powerfulhydrolysing solution that theA solution destroys the stencil. Whensubstances that need such solutions are used the hydrolysis must beperformed before the photographic layer is applied. For instance,cellulose nitrate cannot be employed in the above examples of thevprocess unless the hydrolysis is performed before the photographic layeris applied.

The stencil itself may be formed in any suitable way and not merely inthe way described inthe' example. For instance, a bichromated colloidmay be used instead of a silver halide emulsion, or non-tanningdevelopment of a silver halide emulsion followed by imagewisebichromat'e hardening may be used instead of tanning development. Againany reversal process can be used, such for example as etch-bleachingwith the wellknown solution containing hydrogen peroxide when a negativestencil is formed from a negative original. If necessary the stencil maybe hardened by a hardening agent after being. formed and before beingtreated further.

When a preformed stencil is used it is still preferably photographicallyproduced and it may be transferred in the form of a light-sensitiveemulsion layer containing a latent image, a developed and unxed image ora developed and xed image, or it may be a completely finished stencillayer. In any of these cases, the material that is being transferred maybe soaked and then pressed onto the hydrolysed surface by a squeegee.

As indicated above the invention is useful for other purposes inaddition to printing. As an example a coloured design may be: producedby treating a sheet in which the design areas are cellulose acetate andthe other areas are hydrolysed cellulose acetate with the dyes known asMethyl Violet (Colour Index No. 680)y and Malachite' Green (Colour IndexNo. 657). If it is the hydrolysed areas that are to be colouredpreferentially to areas of cellulose acetate, Cotton Blue (Colour Index706; Schultz No. 816. second volume, 7th edition) (Hopkins and WilliamsLtd), Congo Red (Colour Index No.A 370) and Chrysophenine (Colour IndexNo. 365) may be used. Any of these dyes may be appliedv by simply wipingan aqueous solution of the dye over the sheet.

We claim:

l. A method of producing a printing surface containing a design bytreating a layer of an inkreceptive substance which can be hydrolysed tobe ink-repellent when Wet, characterised in that a surface of the layerthat is in the ink-receptive state is coated With a light-sensitivelayer in which a stencil may be formed by photography, the surface isuniformly hydrolysed to the inkrepellent state, a stencil of the designis photographically produced in the layer coated on the hydrolysedsurface, the hydrolysed material not protected by the stencil is removedto expose inkreceptive areas, and the stencil is then removed to exposethe ink-repellent areas beneath it. 2. A method of producing a printingsurface containing a design by treating a layer of an inkreceptivesubstance which can be hydrolysed to be ink-repellent when wet,characterised in that a surface of the layer that is in theink-receptive state is coated with a light-sensitive layer in which astencil may be formed by photography, this layer is exposed to form alatent image of the design in it, the composite sheet is'then subjectedto the action of a solution which acts simultaneously as a tanningdeveloper and a hydrolysing agent so as to produce a stencilcorresponding to the latent image and to hydrolyse the Whole surfacebeneath the layer containing the stencil to a uniform extent and intothe ink-repellent state, the hydrolysed material not protected by thestencil is removed to expose ink-receptive areas, and the stencil isthen removed to expose the ink-repellent areas beneath it.

3. A method of producing a printing surface containing a design bytreating a layer of an inkreceptive substance which can be hydrolysed tobe ink-repellent when Wet, characterised in that a surface of the layerthat is in the ink-receptive state is coated with a layer of a gelatineemulsion containing a silver halide, a stencil of the design is thenphotographically produced in the emulsion layer, the composite sheet isimmersed in a hydrolysing solution to hydrolyse the surface of the layerof the hydrolysable substance uniformly to the ink-repellent state, thehydrolysed material not protected by the stencil is removed to exposeink-receptive areas, and the stencil is then removed to expose theink-repellent areas beneath it.

4. A method of producing a printing surface containing a design bytreating a layer of cellulose acetate which can be hydrolyzed to beinkrepellent When Wet, characterized in that a surface of said layerthat is in the ink-receptive state is coated with a layer of gelatinemulsion containing a silver halide, a stencil of the design is thenphotographically produced in the emulsion layer, the composite sheet isimmersed in a hydrolyzing solution to hydrolyze the surface of a layerof cellulose acetate uniformly to the inkrepellent state, the hydrolyzedmaterial not protected by the stencil is removed to expose inkreceptiveareas, and the stencil is then removed to expose the ink-repellent areasbeneath it.

5. A method of producing a printing surface containing a design bytreating a layer of cellulose acetate which can be hydrolyzed to beinkrepellent when Wet, characterized in that a surface of said layerthat is in the ink-receptive state is coated with a layer of gelatinemulsion containing a silver halide, a stencil of the design is thenphotographically produced in the emulsion layer, the composite sheet isimmersed in a hydrolyzing solution to hydrolyze the surface of a layerof cellulose acetate uniformly to the inkrepellent state, the hydrolyzedmaterial not protected by the stencil is removed by zinc chloride toexpose ink-receptive areas, and the stencil is then removed to exposethe ink-repellent areas beneath it.

6. A method of producing a printing surface containing a design bytreating a layer of cellulose acetate which can be hydrolyzed to beink-repellent When Wet, characterized in that a surface of said layerthat is in the ink-receptive state is coated with a layer of gelatinemulsion contaning a silver halide, a stencil of the design is thenphotographically produced in the emulsion layer, the composite sheet isimmersed in a hydrolyzing solution to hydrolyze the surface of a layerof cellulose acetate uniformly to the inkrepellent state, the hydrolyzedmaterial not protected by the stencil is removed by a mixture of zincchloride and ethyl lactate to expose ink-receptive areas, and thestencil is then removed to expose the ink-repellent areas beneath it.

'7. A method of forming a design in a printing sheet of an ink-receptivematerial which comprises uniformly hydrolyzing a surface of said sheetto render said surface ink-repellent when wet; selectively removingareas of the surface -that has been uniformly hydrolysed Whileprotecting the remaining areas of said surface by means of a stencil ofan image superposed on the hydrolyzed surface, and thereafter removingthe stencil to expose the protected hydrolysed areas.

8. A method of forming a design in a printing sheet of an ink-receptivematerial which comprises unformly hydrolysing the Whole Working surfaceof a layer of a hydrolysable substance, selectively removing areas ofthe hydrolysed surface While protecting the remaining areas by means ofa stencil of an image superposed on the hydrolysed surface, said removalextending entirely through said surface to expose the inkreceptiveportions of the sheet below said removed areas; and thereafter removingthe stencil to expose the protected hydrolysed areas.

9. A method of producing a printing surface containing a design bytreating a layer of an inkreceptive substance that can be hydrolysed tobe ink-repellent when wet, characterized in that areas of a surface ofthe layer that has been uniformly hydrolysed to be ink-repellent whenWet are selectively removed to leave ink-receptive areas while theremaining areas are protected by a photographically produced stencil ofa design, and the stencil is thereafter removed to expose the protectedhydrolysed areas.

10. A method of producing a printing surface containing a design bytreating a layer of an inkreceptive substance that can be hydrolysed tobe ink-repellent when Wet, characterised in that a stencil of the designis photographically formed in a light-sensitive layer applied to a layerof the hydrolysable substance, the surface being uniformly hydrolysedinto the ink-repellent state in timed relation to the formation of thestencil,

the areas not protected by the stencil are removed to exposeink-receptive areas, and the stencil is thereafter removed to expose theprotected ink-repellent areas.

11. A method of forming a design in a printing sheet of an ink-receptivematerial Which comprises uniformly hydrolyzing a surface of said sheetto render said surface ink-repellent when wet; selectively removingareas of said surface While protecting the other areas by means of aphotographically produced stencil of an image superposed on thehydrolysed surface, said removal extending completely through saidsurface to expose ink-receptive portions below said removed areas; andthereafter removing the stencil to expose the protected hydrolysedareas.

12. A method of producing a printing surface containing a design bytreating a layer of an ink-receptive substance that can be hydrolysed tobe ink-repellent when Wet, characterized in that areas of a surface ofthe layer that has been uniformly hydrolysed to be ink-repellent whenWet are selectively removed to leave exposed inkreceptive areas Whilethe other areas are protected by a photographically produced stencil ofthe design, said layer being thick enough to leave a non-hydrolysedink-receptive layer beneath the hydrolysed surface on being subjected tocontrolled hydrolyses, and thereafter removing the stencil to expose theprotected hydrolysed areas.

13. A printing member comprising, a sheet of a cellulose derivative, ahydrolysed surface on said sheet, said surface being ink-repellent whenwet, portions of said surface corresponding to a design to be printedbeing removed to expose an underlying ink-receptive layer of said sheet.

14. A printing member comprising, a sheet of a cellulose derivative, ahydrolysed surface on said sheet, said surface being ink-repellent whenwet, and portions of said sheet below said surface and corresponding toa design to be printed being of a composition to receive ink.

CHARLES HOWARD MITSON. ERICH EDUARD LOENING.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 556,380 StevensMar. 17, 1896 992,898 Payne May 23, 1911 1,943,486 Ostwald Jan. 16, 19342,013,116 Troland Sept. 3, 1935 2,110,496 Babcock Mar. 8, 1936 2,179,245Wood Nov. 7, 1939 2,276,151 Brandenberger Mar. 10, 1942 2,311,086 SaloFeb. 16, 1943 2,312,499 Lierg Mar. 2, 1943 2,346,008 Clark Apr. 4, 1944FOREIGN PATENTS Number Country Date 3,453- Great Britain Oct. 5, 1875509,010 Germany Oct. 4, 1930 337,868 Great Britain Nov. 13, 1930 385,274Great Britain Mar. 16, 1931 368,083 Great Britain Mar. 3, 1932 599,897Germany July 11, 1934 648,333 Germany July 28, 1937 650,372 GermanySept. 18, 1937 496,049 Great Britain Nov. 21, 1948

7. A METHOD OF FORMING A DESIGN IN A PRINTING SHEET OF AN INK-RECEPTIVEMATERIAL WHICH COMPRISES UNIFORMLY HYDROLYZING A SURFACE OF SAID SHEETTO RENDER SAID SURFACE INK-REPELLENT WHEN WET; SELECTIVELY REMOVINGAREAS OF THE SURFACE THAT HAS BEEN UNIFORMLY HYDROLYSED WHILE PROTECTINGTHE REMAINING AREAS OF SAID SURFACE BY MEANS OF A STENCIL OF AN IMAGESUPERPOSED ON THE HYDROLYZED SURFACE, AND THEREAFTER REMOVING THESTENCIL TO EXPOSE THE PROTECTED HYDROLYSED AREAS.
 13. A PRINTING MEMBERCOMPRISING, A SHEET OF A CELLULOSE DERIVATIVE, A HYDROLYSED SURFACE ONSAID SHEET, SAID SURFACE BEING INK-REPELLANT WHEN WET, PORTIONS OF SAIDSURFACE CORRESPONDING TO A DESIGN TO BE PRINTED BEING REMOVED TO EXPOSEAN UNDERLYING INK-RECEPTIVE LAYER OF SAID SHEET.